Monday, April 7, 2014

Eyes Under Puget Sound: Studying Puget Sound benthos

We have 20 new images of the more than 1,200 unique species of tiny invertebrates, including worms, clams, snails, shrimp, crabs, brittle stars, and many others, that live in the sand and mud at the bottom of Puget Sound.

Scientists refer to these creatures as benthic invertebrates, or benthos, meaning bottom-dwelling.

The benthos are eaten by larger invertebrates such as fish, birds, and gray whales. The tiny animals are an essential link in the Puget Sound food chain.

Ecology scientists study Puget Sound sediment quality to determine whether the sediments support an abundant and diverse community of benthic invertebrates.

We’ve introduced you to the benthos in a recent blog and emphasized their importance in the Puget Sound food web.

But how do we collect, study, and sort out this diverse group of animals that live their lives buried in the mud?

Gotta catch ‘em all!

Sediment and benthos samples are collected by our scientists each year from different regions and urban bays throughout Puget Sound.Working from a research vessel, we use a stainless-steel double van Veen grab sampler to collect bottom sediments from selected station locations.

Consisting of two single grabs that are joined together, the sampler works like a giant claw. With the claw open, the grab is lowered from a winch to the bottom of the Sound. When it hits the bottom, it snaps shut, collecting a 0.1 square meter x 17 cm “bite” of the sand and mud.

Sediments are collected from one of the paired grabs for chemical and bioassay testing, while the sand and mud from the other grab is washed through a 1mm mesh screen to remove all benthos living within them.

Gotta sort ‘em all!

Puget Sound sediment sample.

The sieved benthos are brought back to the lab, where they are examined under a microscope and sorted into four dominant phyla (a phylum is a major category used to classify organisms) and a miscellaneous grouping for all remaining benthos phyla. The four dominant phyla are Annelids, Molluscs, Arthropods, and Echinoderms.

Gotta name and count ‘em all!

You can’t understand or protect what you can’t keep track of!

To study and understand the dynamics of the benthic invertebrate communities in Puget Sound, Ecology’s marine sediment monitoring scientists must know which benthic species are living at each station, and in what numbers.

An average sediment station grab contains about 50 of the over 1,200 Puget Sound invertebrate taxa, and around 600 animals (but can range from less than 100 to over 1000). It is no small task to name and count every animal found in each sample!

Taxonomy — What’s in a name?

Taxonomy is the science of grouping and ranking organisms based on shared physical and genetic features, and then assigning a hierarchical series of names (scientific classification) to each unique group of organisms. Progressing from broadest to most specific, organisms are assigned to the categories Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Scientists typically refer to each unique type of organism using binomial nomenclature, or a two-part naming system, which includes only the Genus and species. For example, humans are known as Homo sapiens, Orca whales as Orcinus orca, and Dungeness crab as Metacarcinus magister.

Taxonomists are scientists who specialize in (what else?) the taxonomy of different groups of organisms. Ecology’s sediment team works with a small number of regional taxonomists, each a specialist in identification of one major group of Puget Sound benthos.

It takes patience

Our taxonomists patiently and meticulously examine each organism collected from our sediment samples. Then, with their intimate knowledge of the number and shape of the many spines, palps, tentacles, and other assorted body parts that define each species, they carefully assign a name to, and count each animal, generating a set of benthos data for all of the sampled sediments.

A lost science?

There are very few taxonomists who can identify Puget Sound benthos to the species level. Only one or two local experts currently specialize in the taxonomy of each of the major phyla, and very few students in our universities are learning this craft. Our sediment team is worried about continued monitoring of benthos when these specialists retire, and so we are working to record this taxonomic knowledge to use well into the future.

Recent declines seen in the condition of Puget Sound benthic communities

Marine monitoring website and info

More details about the sediment quality and benthos in Puget Sound’s regions and bays can be found on the
Marine Sediment Monitoring Team’s website, along with information on the design and implementation of the Puget Sound Ecosystem Monitoring Program (PSEMP) sediment monitoring component.

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